1. Field of the Invention
The present invention relates to a wear resisting aluminum alloy composite material.
2. Description of the Related Art
In general, rotors and vanes and so on of a rotary compressor slide and rotate in a rotary cylinder. Improved sliding characteristics as well as light weight have been required for the sliding members used at higher speeds. Therefore, various composite materials which comprise an aluminum alloy including reinforcing fibers as reinforcement have been developed as shown in the prior arts explained below.
JP-A-4-350135 discloses a combination of sliding members such as a vane member and a rotor member for a rotary compressor, in which the first member is made of an aluminum composite siding material comprising a hybrid compact of both aluminum borate whisker and alumina fiber which hybrid compact is impregnated with aluminum alloy. The second member is made of a cast iron material which is perforated for reducing the weight thereof. In the first sliding member, the mixing ratio of the aluminum borate whisker to the alumina fiber is in the range of 0.5 to 2.0, and the impregnated aluminum alloy contains 20 to 30% silicon. In the first prior art, it is disclosed that, by using the combination, it becomes possible to reduce the damage of a cast iron counterpart member, that is, to reduce the attacking property of the first member against the counterpart member.
In the first member of the first prior art (JP-A-4-350135) which is made of the hybrid compact comprising an aluminum borate whisker and an alumina fiber, the formability of the hybrid compact is obtained by mixing 33 to 67% alumina fiber. However, the sliding member of the hybrid compact impregnated with the aluminum alloy has such a drawback as the sliding member severely attacks a counterpart member due to high hardness of the alumina fiber. Furthermore, 20 to 30% by weight of silicon, which is added in the impregnated aluminum alloy in order to obtain wear resistance and low thermal expansion, causes low toughness of the alloy due to hard and brittle coarse primary crystal silicon particles precipitated therein.
JP-A-4-350136 discloses a sliding material comprising 20 to 80% by volume of reinforcing fiber which is a mixture of both aluminum borate whisker and aluminum fiber and which is impregnated with an aluminum alloy. The sliding member of the second prior art also causes unfavorably severe attacking against a counter-part member because the hybrid compact may contain 20 to 80% of alumina fiber.
These conventional hybrid compacts do not bring about satisfactory sliding characteristics, such as anti-seizure property and wear resistance, because the high content of the alumina fiber is mixed in the hybrid compact in order to obtain shape-keeping-property (, that is, rigidity).